The instant invention relates to thermally responsive control devices and more particularly to a thermally responsive electrical control device and to a monitoring circuit which is operable in combination therewith.
A number of types of thermally responsive control devices have heretofore been available for various applications. In this connection, one common type of thermally responsive control device heretofore available is a type commonly referred to as an electromechanical control device which utilizes the thermal expansion of a fluid contained therein for actuating contacts. Devices of this type, however, have only been operative over limited temperatures ranges which are usually less than 100.degree. F. and have displayed only marginal degrees of accuracy. They have also not provided any means for displaying or indicating sensed temperatures. A number of inexpensive electronic control devices have also been heretofore available, but these devices have also only been operable over limited temperature ranges, such as ranges of between 50.degree. and 100.degree. F. and have not had high degrees of accuracies because they have depended on the accuracies of components connected thereto. Most of these devices have only been operative for performing single control functions for each sensed temperature, and any of the heretofore available devices of this type which have been operative for multiple control functions have only been adapted for limited applications. In addition, most of the heretofore available control devices of this type have not been operable in combination with means of providing visual indications of sensed temperatures. In this regard, the only heretofore available electronic control devices of this type which have been operable in combination with means for providing visual temperature displays have required on and off switching functions. Specifically, they have required switched interruptions in the controlling functions thereof during monitoring operations so that they have been inoperative for controlling during the periods when the temperatures are monitored for visual indications. This type of operation is undesirable for many control systems. Thermally responsive electronic controls having internal microcomputer components have also been heretofore available and have proven to be effective for a number of applications, however, controls of this type have been relatively expensive, and therefore their use has been somewhat limited by this factor.
The instant invention provides an effective thermally responsive electrical control device which is operable in combination with the monitoring circuit of the instant invention for providing a control and monitoring device which overcomes many of the disadvantages of the known devices. The control device of the instant invention is operative for providing multiple control functions in response to single sensed temperatures, and when it is combined with the monitoring circuit of the instant invention, visual indications of sensed temperatures can be provided as well as visual indications of control parameters. The visual indications provided by the monitoring circuit allow the control parameters to be set with high degrees of accuracy which could heretofore only be achieved with control devices having internal mircroprocessor components. In this connection, while the monitoring circuit of the instant invention does include microprocessor components, the control device of the instant invention by itself does not. Hence, the construction of the control device of the instant invention is relatively economical compared to the heretofore available control devices having internal microprocessor components. Although the monitoring circuit of the instant invention includes microprocessor components, a single monitoring circuit can be interconnected at different times with different control devices for monitoring respective sensed temperatures, and hence the overall cost for providing an effective system which includes several thermally responsive control devices is substantially reduced when used in combination with the monitoring circuit.
The thermally responsive control device of the instant invention provides a novel and effective means for measuring and indicating temperatures sensed in a bridge circuit. Further, one embodiment of the thermally responsive control device includes a novel bridge circuit wherein three control decisions are effected in response to two sensed temperatures. In another embodiment of the thermally responsive control device of the instant invention, the inherently nonlinear characteristic of a thermistor is compensated for by matching the thermistor with a nonlinear potentiometer so that a substantially linear relation is achieved between the temperature sensed by the thermistor and the degree of movement or manipulation required for changing the resistance of the potentiometer. Accordingly, for these reasons, as well as a number of other reasons which will hereinafter be made apparent, it is seen that the instant invention provides a significant advancement in the electrical art which has substantial commercial merit.
Accordingly, it is an object of the instant invention to provide an effective combination of a thermally responsive control device and a monitoring circuit for providing an effective thermally responsive electrical control as well as visual indications of sensed temperatures.
Another object of the instant invention is to provide a thermally responsive electrical control device wherein a plurality of control decisions are effected in response to a single sensed temperature.
Another object of the instant invention is to provide a thermally responsive control device which comprises a thermally responsive thermistor, wherein the inherent nonlinear characteristic of the thermistor is compensated for by the use of a potentiometer having a corresponding nonlinear characteristic.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.